Control apparatus for well tool anchor



Aug. 29, 1967 H. L. MCGILL 3,338,309

CONTROL APPARATUS FOR WELL TOOL ANCHOR Filed Aug; 9, 1965 2 Sheets Sheet 1 Howard 1. Mc6/// INVENY UR.

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Aug. 29, 1967 H. L. MCGILL 3,338,309

CONTROL APPARATUS FOR WELL TOOL ANCHOR Filed Aug. 9, 1965 2 Sheets-Sheet 2 2/! Z5 Z6 A. :1 7a m r g M fl Z43 79 I w 42 5 I i 17 z 7 5x 15 S 3 l 440 52 f 3 70 3 86 L' q; 37 E .92 a 9 j 38 i s .96 94 2a 93 K0 4 36 J4 a i a J- J- Howard 1. MC G'/// INVENTOR.

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ATTORNEY United States Patent Office 3 ,3'3 8,3 6 g Patented Aug. 29, 1 967 3,338,309 CONTROL APPARATUS FOR WELL TOOL ANCHOR Howard L. McGill, Houston, Tex., assignor, by mesne assignments, to Schlumberger Technology Corporation, Houston, Tex, a corporation of Texas Filed Aug. 9, 1965, Ser. No. 478,218 6 Claims. (Cl. 166122) This invention relates generally to apparatus adapted for operation in a well bore and more particularly, to control apparatus for an hydraulically actuated anchor for wells, which anchor, when set in place, will hold the tool fixed against well pressures acting from either direction by an anchoring force proportionately related to the acting pressure.

In conducting such well-completion operations as acidizing, cementing, or facturing, a full-opening well packer dependently coupled from a tubing string is positioned at a particular depth in a cased well and the packer set to isolate the formation interval to be treated from the remainder of the well bore thereabove. Treating fluids are then pumped downwardly at high pressure through the tubing and packer and introduced to the formation being treated through perforations appropriately located in the casing. In those instances where a well having several producing formations is being completed, a selectively operable bridge plug can be dependently coupled beneath the full-opening packer. Such a bridge plug permits packing-off of zones of selected length in the well bore for selective treatment of different formation intervals with only a single trip into the well.

It will be appreciated that such packers and bridge plugs must be capable of withstanding high pressures acting from either direction. Furthermore, during the course of typical completion operations, a packer and bridge plug are usually subjected to high pressures acting alternately from both above and below. Thus, it is necessary to securely anchor such apparatus against movement in either longitudinal direction.

Accordingly, it is an object of the present invention to provide new and improved apparatus for controlling hydraulically actuated wall-engaging anchoring means for well tools, which means are pressed into anchoring engagement with a force proportionately related to the pressure of the well fluid.

A bridge plug employing the control apparatus of the present invention includes selectively operable wall-engaging means including a hydraulic system which, in response to the pressure of well fluids, are arranged to be pressed into anchoring engagement with the wall of the well bore. To secure the bridge plug for actuation of the wall-engaging means, spring-biased piston means are provided for developing a hydraulic pressure that is suflicient to frictionally engage the wall-engaging means with the .wall. Selectively operable means are provided for deactivating the spring-biased means, which selective means are operable at a predetermined pressure to activate the spring biased means whereby a sufficient hydraulic pressure will be developed to frictionally engage the wall-engaging means with the wall with a predetermined force.

The novel features of the present invention are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation together with further objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a view of a full-bore packer and a bridge plug including the control apparatus of the present invention and depicted as they would appear within a well bore;

FIGS. 2A, 2B, and 2C are successive, detailed crosssectional views of an embodiment of a bridge plug havingthe control apparatus of the present invention;

FIG. 3 is a cros-s-sectonal view taken along the line 3-3 of FIG. 2B; and

FIG. 4 is a view showing particular details of a valve employed with the bridge plug of FIG. 2.

As seen in FIG. 1, a typical full-bore packer 10 is dependently connected to a tubing string 11 and p0si tioned within the well bore 12 having a casing 13 set therein. A retrievable bridge plug 14 is shown within the casing 13 and releasably coupled to the overshot 15 dependently connected beneath the well packer 10 by a fishing neck 16 on the bridge plug. This releasable coupling allows the bridge plug 14 to be set at the lower limit of a particular formation interval and the packer 10 subsequently set at any point thereabove irrespective of the length of the tubing sub 17 connecting the packer to the bridge plug.

Turning now to FIGS. 2A2C, the retrievable bridge plug 14 depicted in FIG. 1 includes a movable mandrel 18 telescopically arranged within a tubular housing 19. Oppositely directed elastomeric packing cups 20 and 21 are mounted around the upper end of the housing 19 and separated from one another by elastomeric back-up rings 22 and 23. Whenever there is a pressure differential across the cups 20 and 21, one or the other of them will be expanded outwardly into sealing engagement with the casing 13.

For establishing the longitudinal position of the mandrel 18 relative to the housing 19, an outwardly projecting lug 24 on the central portion of the mandrel is slidably received within a generally T-shaped slot system 25 formed in the adjacent internal housing wall. The slot system 25 is comprised of an elongated longitudinal slot 26 that is parallel to a short slot 27 and interconnected at their centers by a circumferential slot portion 28. Th s, so long as the lug 24 is confined within the shorter slot portion 27, the mandrel 18 cannot shift appreciably in either longitudinal direction relative to the housing 19 and is, therefore, less susceptible to inadvertent release as it is being positioned in a well bore. The mandrel 18 is torqued to the right to move the lug 24 through the connecting slot 28 into the longer longitudinal slot 26. Once the lug 24 is shifted into the longer slot 26, the mandrel 18 is free to shift longitudinally an appreciable distance relative to the housing 19.

A hydraulically actuated, radially expansible friction anchor 29 is arranged and mounted around the central portion of the housing 19. The friction anchor 29 is adapted to be pressed against the casing 13 to initially hold the housing relatively fixed against rotation of the mandrel 18 as well as to subsequently anchor the bridge plug 14 against pressure differentials acting from either direction. This anchor 29 includes an elastomeric sleeve 30 encircling the housing 19 with a plurality of elongated casing-engaging members 31 and 32 being mounted uniformly around the periphery of the sleeve. The enlarged upper and lower ends 33 and 34 of the elastomeric sleeve 30 are sealingly secured within opposed annular recesses 35 and 36 around the housing 19 to provide a fluid-tight space 37 between the sleeve and housing.

Each of the casing-engaging members 31 and 32 are elongated and have a thick, arcuate, cross-section (FIG. 3). Alternate ones 31 of these casing-engaging members are centrally aligned and mounted along the outer convex surface of relatively thin, elongated, arcuate backing members 38. The mounted members 31 are arranged uniformly around the periphery of elastomeric sleeve 30 so that the backing members 38 substantially encompass the sleeve. The unmounted casing-engaging members 32 are alternately disposed between the mounted casing-engaging members 31 in such a manner that the unmounted members 32 straddle adjacent backing members 38 and cover the gap 39, therebetween. The beveled ends of the casing-engaging members 31 and 32 are loosely disposed within the opposed annular recesses 35 and 36 around the housing 19 at opposite ends of the members.

A central axial bore 40 extends the full length of the mandrel 18 and is capped at its upper end by a suitable fishing neck 16. The fishing neck 16 is arranged for cooperatively receiving a tubular overshot 15 which may be dependently coupled to either the full-bore packer or the tubing string 11. Matched J-slots 41 on opposite sides of the fishing neck 16 are arranged to receive cooperatively arranged I-pins 42 projecting radially inwardly from the overshot whenever the overshot is lowered over the fishing neck. After the J-pins 42 enter the open upper end of the long portion of the slots 41, the pins are lockingly engaged in the closed short portion of the slots by a concerted application of left-hand torque and a slight upward pull on the tubing 11. Conversely, the overshot 15 is selectively disengaged from the fishing neck 16 by lowering the tubing 11 slightly, torquing the tubing to the right, and then pulling upwardly.

Radial ports 43 in the upper end of the mandrel 18 and ports 44 in the lower end of housing 19 allow fluids in the well bore to bypass the packing cups and 21 as the bridge plug 14 is being shifted within a fluid-filled well bore. Thus, the packing cups 20 and 21 are prevented from becoming sealingly engaged against the casing 13 which otherwise could retard or even prevent shifting of the bridge plug 14.

Fluid communication through lateral equalizing ports 43 above the packing cups 20 and 21 is selectively controlled by .an annular valve member 45 which is slidably disposed around the mandrel 18 immediately adjacent the ports. When the valve member 45 is in its lowermost position as shown in FIG. 2A, ports 46 are brought into register with the upper mandrel ports 43 to permit fluids to flow therethrough. However, when the valve member 45 is pulled upwardly to about the lower surface of the overshot 15, the valve member ports 46 are moved out of registry with ports 43 and O-rings 47 .and 48 around the mandrel 18 above and below the mandrel ports 43 will sealingly engage the lower portion of the valve member to block fluid communication therethrough. Thus, it will be apparent that the slidable valve member 45 is cooperatively arranged to be longitudinally shifted by the overshot 15 so that the equalizing ports 43 are uncovered whenever the overshot is engaged over the fishing neck 16 and covered whenever the overshot is removed.

Whenever the valve member 45 is pulled upwardly, depending resilient fingers 49 around the lower end of the valve member are cammed outwardly as they pass over an annular shoulder 50 around mandrel 18 and then retracted after clearing the shoulder. The lower ends 51 of these fingers 49 will then engage the upwardly facing portion of the annular shoulder 50 to hold the slidable valve member 45 in its upper most or port-closing position after overshot 15 has been removed.

A shoulder 52 projecting inwardly from the central portion of the overshot 15 is arranged to engage the upper end of valve member 45 and shift the valve downwardly to its open position as the overshot is being coupled over the fishing neck 16. Whenever the overshot 15 is removed by torquing it to the right and picking up, a group of resilient fingers 53 spaced around the lower portion of the overshot 15 have inwardly projecting shoulders 54 arranged to engage a shoulder 55 on the sliding valve member 45 to pull it upwardly and close the equalizing ports 43.

Whenever it is desired to move the bridge plug 14, the overshot 15 is dropped over and re-engaged with the fishing neck 16. As the overshot 15 is being lowered over the fishing neck 16, the slidable valve member 45 is, of course, again shifted downwardly to reopen the equalizing ports 43 and equalize pressure across the packing cups 20 and 21.

It will be appreciated that when the usual bridge plug of the type illustrated is being shifted downwardly in the fluid-filled well bore, a pressure differential may develop between fluids trapped in the annular space between the packing cups and the well fluids surrounding the tool above and below the packing cups. Such pressure diflerential tends to expand the cups into sealing engagement with the casing wall resulting in a swabbing action which can damage the packing cups and deleteriously affect the speed at which the bridge plug can be lowered into the well. To eliminate this swabbing action, means are provided in the bridge plug 14 for equalizing fluid pressure between the cups 20 and 21 with that of the fluids above and below the cups so long as the mandrel lug 24 is confined within the shorter slot 27. To accomplish this, as seen in greater detail in FIG. 4, an inwardly biased valve member 56 having an axial passage 57 is slidably disposed in a hollowed valve body 58 that is closed at its outer end and fluidly sealed within a lateral bore 59 through the housing 19 between the cups 219 and 21. When the valve member 56 is in one position, O-rings 69 and 61 around the valve member are arranged to be spaced inwardly and outwardly of the port 62 through the valve body 58 and opening to the exterior of the housing 19 between the cups 20 and 21.

A flat surface (FIG. 2A) formed across the mandrel 18 is so aligned that whenever the mandrel lug 24 is confined within the shorter housing slot 27, the inner end 64 of the valve member 56 is engaged with the mandrel flat. With the valve member 56 in this position, the valve member and O-ring 61 are displaced inwardly from the port 62 to admit fluids in the well through the lateral housing passage 65 below the packing cups 20 and 21 into the clearance 66 between the mandrel 18 and the housing 19 to equalize the pressure between the cups. When the mandrel 18 is manipulated to bring the mandrel lug 24 into the elongated slot 26, the inner end 64 of the valve member 56 will be cammed outwardly by the peripheral surface of the mandrel adjacent to the flat 63. Thus, once the mandrel 18 has been rotated to bring the lug 24 into the elongated slot 26, the valve member 56 will be shifted to its outermost position shown in FIG. 4 and sealed by O-rings 60 and 61 to block fluid communication between port 62 and axial passage 57.

Turning now to the hydraulic system of the friction anchor 29, the housing 19 is formed in such a manner as to provide an annular chamber 67 (FIG. 2B)v above the upper end of the anchor. A similar annular chamber 68 (FIG. 2C) is also formed below the lower end of the anchor 29. The annular clearance space 69 between the mandrel 18 and the housing 19 provides fluid communication between the upper chamber 67 and lower chamber 68. A plurality of radial ports 70' through the housing 19 adjacent the elastomeric sleeve 30 provide fluid communication from this clearance 69 to the sealed space 37 underneath the elastomeric sleeve.

The upper end of the upper annular chamber 67 and lower end of the lower annular chamber 68 are respectively closed by annular piston members 71 and 72 which are slidably mounted therein and fluidly sealed by O-rings '7376 to both the housing 19 and the mandrel 18. The upper slidable piston member 71 is free to move downwardly in the upper chamber 67 until reaching an upwardly directed housing shoulder 77 therein. The lower slidable piston member 72 is normally biased downwardly by a spring 78 against an upwardly directed shoulder 79 formed in the housing 19 at the lower end of the lower chamber 68.

The mandrel 18 has a shoulder 80 formed thereon, the

' shoulder being located a short distance above the upper slidable piston 71. Shoulder 80 is suitably arranged to engage the upper piston and force it downwardly whenever the mandrel 18 shifts downwardly. Similarly, a second mandrel shoulder 81 is located below the piston 72 and is adapted to engage and shift the lower piston member upwardly whenever the mandrel 18 shifts in that direction. It will be appraciated, therefore, that with a suitable fluid in the above-described hydraulic system, longitudinal shifting of the mandrel 18 in either direction will expand the elastomeric sleeve 30 of the anchor 29 and press the casing-engaging members 31 and 32 against the casing 13.

A compensating chamber 82 is formed in the housing 19 below the lower piston member 72 to maintain a supply of fluid in the hydraulic system as well as to compensate for thermal expansion of the fluid. The lower end of this compensating chamber 82 is closed by a slidable annular compensating piston member 83 having O-rings 84 and 85 around its inner and outer surfaces which, in conjunction with a seal ring on the lower portion of mandrel 18, fluidly seal the compensating piston relative to the housing 19 and the mandrel 18.

For reasons that will subsequently become apparent, a sleeve 86 is slidably disposed within the lower end of the housing 19 and releasably secured thereto by a frangible shear member, such as pin 87 or the like, to hold an upper shoulder 88 of the sleeve 86 a short distance below the compensating piston 83. A compression spring '89 is mounted around the sleeve 86 and is confined between an upwardly directed housing shoulder 90 and a downwardly directed shoulder on sleeve 86. An annular piston member 91 having a reduced-diameter upper portion 92 and an enlarged-diameter lower portion 93 is slidably disposed within the housing 19 below the shear member 87. O-rings 94 and 95, respectively, around the enlarged and reduced portions 93 and 92 of the release piston 91 are spaced from one another and fluidly seal the piston relative to the housing 19 to define an enclosed, sealed space 96 therebetween.

Selectively controlled fluid communication is provided between the compensating chamber 82 and the remainder of the hydraulic system through a housing passage 97 and an annular clearance space formed by a reduced-diameter portion 98 around the mandrel 18. This reduced-diameter portion 98 is arranged to be in juxtaposition with the lower piston 72 Whenever the mandrel 18 is in its intermediate position as determined by the mandrel lug 24 being confined within the shorter slot 27. When, however, the mandrel 18 is so manipulated to shift the lug 24 into the longer slot 26 and the mandrel is shifted longitudinally only a slight distance in either direction, the inner O-ring 75 within the lower piston member 72 fluidly seals piston to the adjacent surface of the mandrel at either 99 or 100 depending upon the direction in which the mandrel has been shifted.

Accordingly, it will be seen that so long as the mandrel 18 is in a neutral or intermediate position (as determined by the lug 24 being within the short slot 27), the mandrel is substantially restrained from shifting longitudinally in either direction and the upper and lower piston members 71 and 72 will be substantially in the positions illustrated in FIG. 2 with the mandrel shoulders 80 and 81 separated therefrom. When the mandrel 18 is in the above-mentioned intermediate position, there will be free fluid communication (by way of the reduced-diameter mandrel portion 98) of the hydraulic fluid from the compensating chamber 82 into the remainder of the hydraulic system.

Turning now to the operation of the bridge plug 14, it will be apparent that when the mandrel lug 24 is shifted Within slot system 25, means must be provided to hold the housing 19 fixed relative to the mandrel 18. Moreover, after the bridge plug 14 has been set, the housing 19 must remain anchored to the casing 13 with a minimum holding force either when the mandrel 18 is not sutficiently displaced to coact with one of the pistons 71 and 72 or when the mandrel is being shifted through an intermediate position to one of the other positions. It will be recognized, of course, that were the lower spring 89 always engaged with the compensating piston 83, the compensating piston would be urged upwardly to develop a pressure in the hydraulic system that was proportionately related to the spring force. Thus, by selecting a suitable spring rate for the spring 89, a predetermined hydraulic pressure would be developed to maintain the wall-engaging members 31 and 32 engaged against the casing 13 with a holding force that is adequate to accomplish the abovedescribed functions.

Although this approach is successful in some operations, it has been found difficult in other instances to shift a bridge plug arranged in this manner downwardly in the well bore before it has reached a depth where the tubing string has suflicient weight to overcome the abovementioned holding force. Inasmuch as the minimum holding force may well be in the order of a few thousand pounds, it will be recognized that, in some instances, several hundreds of feet of tubing will be required before the weight of the assembled tubing string will freely shift the bridge plug downwardly.

Accordingly, the bridge plug 14 of the present invention, includes means for initially removing the spring bias from the compensating piston 82 until such time that the bridge plug 14 has reached a predetermined depth in a well bore. To accomplish this, the retainer sleeve 86 is secured at its lower end to the housing 19 by the shear pin 87 to depress the spring 89 below the compensating piston 83. By spacing the retainer sleeve 86 below the compensating piston 83, the compensating piston is free to move downwardly to accommodate thermal expan sion of the hydraulic fluid within the system as the bridge plug 14 is lowered into warmer environments.

To release the retainer sleeve 86, the stepped release piston 91 immediately below shear pin 87 is appropriately arranged to move upwardly and into engagement with the lower end of the retainer sleeve in response to the hydrostatic pressure of fluids in the well bore. It will be appreciated that as the bridge plug 14 is assembled at the surface, the space 96 between O-rings 94 and will be at atmospheric pressure. Thus, as the hydrostatic pressure increases during the descent of the bridge plug 14, it will act upon the efiective cross-sectional area between O-rings 94 and 95 to urge the release piston 91 upwardly against the lower end of the retainer sleeve 86 with a force proportionately related to the hydrostatic pressure. Then, whenever the bridge plug 14 has reached a depth at Which the hydrostatic pressure is suflicient to enable the release piston 91 to shear the pin 87, the retainer sleeve 86 will be released from the housing 19 and be carried upwardly by the compensating spring until the upwardly directed shoulder 88 engages a downwardly directed shoulder on compensating piston 83 immediately below the O-ring 84. Once the compensating spring 89 has been released, it will be appreciated that it will urge the compensating piston 83 upwardly with a predetermined force calculated to develop suflicient hydraulic pressure within the system to move the casing-engaging members 31 and 32 outwardly against the casing 13 with a desired holding force.

When the bridge plug 14 has been positioned at the depth at which it is to be set, it is halted and the overshot moved as previously described. As the overshot 15 is removed, the valve member 45 closes the equalizing ports 43 and the mandrel 18 is shifted upwardly relative to the housing 19 to first sealingly engage the O-ring 75 within the lower piston 72 at on the mandrel and, thereafter, bring lower mandrel shoulder 81 against the lower piston and shift it upwardly. As the lower piston 72 is shifted upwardly, it will be appreciated that a hydraulic pressure will be developed within the hydraulic system to expand the casing-engaging members 31 and 32 against the casing 13 with still greater force.

It will be recognized, of course, that after the overshot 15 has been disengaged from the fishing neck 16, the

mandrel 18 is free to shift longitudinally within the limits determined by the length of the longitudinal housing slot 26. Any pressure difierential across the packing cups 20 and 21 will also act on the mandrel 18. Should the pressure in the well bore above the bridge plug 14 be greater than the pressure below, the pressure differential will act on the upwardlyiacing cup 20 as well as tend to shift the mandrel 18 downwardly. Downward shifting of the mandrel 18 will cause shoulder 86 to drive the upper slid able piston member 71 downwardly, which action will result in increasing the hydraulic pressure within the systern to press the casing-engaging members 31 and 32 of the friction anchor 29 against the well casing 13 with a force which is proportionately related to the pressure differential across the bridge plug 14.

Should, perchance, the pressure in the well bore below the bridge plug 14 become greater than the pressure thereabove, the mandrel 18 will be shifted upwardly. As the mandrel 18 shifts upwardly, the hydraulic pressure will be momentarily reduced as the upper piston member 71 returns to its initial position against housing shoulder 77. Moreover, as the reduced-diameter mandrel portion 98 passes upwardly relative to O-ring 75 within the lower piston 72, there will be a momentary resumption of fluid communication between the hydraulic system and the compensating chamber 82. At this point, however, the force of the compression spring 89 will be sufficient to maintain the pressure within the hydraulic system at a suificient magnitude to maintain the wall-engaging members 31 and 32 firmly secured against the casing 13. Then, as the mandrel 18 continues to travel upwardly, the reduced-diameter mandrel portion 98 will move upwardly relative to the lower piston 72 which will then itself be shifted upwardly by the lower mandrel shoulder 81. As the mandrel 18 continues its upward movement hydraulic pressure will again be increased within the fluid-filled hydraulic system to again urge casing-engaging members 31 and 32 against the casing 13 with a force that is proportionately related to the pressure differential across the bridge plug 14.

To release the bridge plug 14, it is necessary only to re-engage the fishing neck 16 with overshot 15. As the overshot 15 moves over the fishing neck, the equalizing valve member 45 is again shifted downwardly to bring ports 46 thereon into registry with mandrel ports 43. With the fluid pressure equalized across the retrievable bridge plug 14, the mandrel 18 is shifted to its intermediate position and torqued to the left to return the mandrel lug 24 through spot 28' into the housing slot 27. It will be appreciated that as the mandrel lug 24 is being rotated through slot 28, the valve member 56 between the packing cups 20 and 21 will again be cammed open as the flat surface 63 on the mandrel 18 is rotated again under the valve member end 64-. Thus, with the mandrel 18 rejayed, the retrievable bridge plug 14 can now be removed from the well bore.

It will be understood, of course, that as the retrievable bridge plug 14 is being shifted, the compensating spring 89 will remain engaged with the compensating piston 83. Thus, the wall-engaging members 31 and 32 will still be held against the casing with the predetermined holding force as previously described. This will present no problem in shifting the bridge plug 14 in either direction inasmuch as the tubing string 11 can be pulled upwardly with more than suflicient force to overcome this predetermined holding force and the weight of the tubing string at this depth will still be sufficient to move the bridge plug downwardly. Thus, should it be desired to position the bridge plug 14 at a different depth without first removing it from the well bore, it is only necessary to halt the bridge plug at the desired position and repeat the above-described setting operation. Then, when it is desired to finally retrieve the bridge plug, it is necessary only to repeat the abovedescribed retrieving operation and remove the bridge plug 14 from the well bore.

Accordingly, it will be appreciated that the present invention provides a positive control for a hydraulically actuated anchor for a well tool. Where such a tool is a retrievable bridge plug, the cooperative arrangement disclosed herein will allow the bridge plug to be easily positioned within a well bore and then selectively actuated to set the bridge plug into sealing engagement with the casing. The arrangement of the present invention allows the bridge plug to be first frictionally secured to the casing with a force that is sufficient to permit manipulation of its mandrel. Then, once the bridge plug is set, it will remain anchored against the casing with a force proportionately related to the pressure diiferential acting across it. The arrangement further maintains the hydraulic system at any desired pressure regardless of ambient conditions within the well.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made without depart ing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A retrievable bridge plug sized and adapted for reception in a well bore comprising: telescoping inner and outer members, said members being relatively movable between upper, lower and intermediate locations, said members having a space therebetween and sealing means between said members, pack-off means on one of said members, hydraulically actuatable wall-engaging means on said outer member and having fluid communication to said space, upper and lower slidable piston means in said space, a fluid in said space whereby said piston means may apply pressure to said wall-engaging means, means on one of said members selectively cooperating with one or the other of said pistons in said upper and lower locations to apply pressure, means for releasably holding said members in said intermediate location, passage means through said inner member, valve means for selectively closing said passage, a closed chamber containing fluid, piston means in said chamber, spring means for acting on said last-mentioned piston means for applying pressure to the fluid in said closed chamber, bypass means operative only in said intermediate location for placing said closed chamber in fluid communication with said space, and means for selectively operating said last-mentioned piston means.

2. A retrievable bridge plug sized and adapted for reception in a well bore comprising: telescoping inner and outer members, said members being relativelymovable between upper, lower and intermediate locations, said members having a space therebetween and sealing means between said members, pack-off means on one of said members, hydraulically actuatable wall-engaging means on said outer member and having fluid communications to said space, upper and lower slidable piston means in said space, a fluid in said space whereby said piston means may apply pressure to said wall-engaging means, means on one of said members selectively cooperating with one or the other of said pistons in said upper and lower locations to apply pressure, means for releasably holding said members in said intermediate location, passage means through said inner member, valve means for selectively closing said passage, a closed chamber containing fluid, piston means in said chamber, spring means for acting on said last-mentioned piston means for applying pressure to the fluid in said closed chamber, bypass means operative only in said intermediate location for placing said closed chamber in fluid communication with said space, and pressure-responsive means norm-ally holding said spring means inoperative, said pressure-responsive means requiring a predetermined pressure for operation.

3. A retrievable bridge plug sized and adapted for reception in a well bore comprising: telescoping inner and outer members, said members being relatively movable between upper, lower and intermediate locations. said members having a space therebetween and sealing means between said members, pack-off means on one of said members, hydraulically actuatable wall-engaging means on said outer member and having fluid communication to said space, upper and lower slidable piston means in said space, a fluid in said space whereby said piston means may apply pressure to said wall-engaging means, means on one of said members selectively cooperating with one or the other of said pistons in said upper and lower locations to apply pressure, means for releasably holding said members in said intermediate location, passage means through said inner member, valve means for selectively closing said passage, a closed chamber containing fluid, piston means in said chamber, spring means for acting on said last-mentioned piston means for applying pressure to the fluid in said closed chamber, bypass means operative only in said intermediate location for placing said closed chamber in fluid communication with said space, shear means releasably connecting said spring means to said outer member, and pressure-responsive means on said housing operable at a predetermined pressure for releasing said shear means.

4. A well tool comprising: a support, pressure-responsive means on said support, hydraulic means for operating said pressure-responsive means including a closed hydraulic chamber, piston means in said chamber, spring means for acting on said piston means for applying pressure to said closed chamber, and disabling means normally preventing said spring means from acting on said piston means, said disabling means being operative in response to predetermined pressure in a well bore.

5. A well tool comprising: a support, pressure-responsive means on said support, hydraulic means for operating said pressure-responsive means including a closed hydraulic chamber, piston means in said chamber, spring means for acting on said piston means for applying pressure to said closed chamber, and pressure-responsive means normally holding said spring means inoperative, said pressure-responsive means requiring a predetermined pressure for operation.

6. A well tool comprising: a support, pressure-responsive means on said support, hydraulic means for operating said pressure-responsive means including a closed hydraulic chamber, piston means in said chamber, spring means for acting on said piston means for applying pressure to said closed chamber, shear means releasably conmeeting said spring means to said support, and pressureresponsive means on said member operable at a predetermined pressure for releasing said shear means.

References Cited UNITED STATES PATENTS 2,845,127 7/1958 Breaux l66120 X 2,925,128 2/1960 Page 166 212 X 3,254,722 6/1966 Chenoweth 166-120 3,305,022 2/1967 Kisling 166-122 3,306,360 2/1967 Young 166120 CHARLES E. OCONNELL, Primary Examiner.

30 DAVID H. BROWN, Examiner. 

4. A WELL TOOL COMPRISING: A SUPPORT, PRESSURE-RESPONSIVE MEANS ON SAID SUPPORT, HYDRAULIC MEANS FOR OPERATING SAID PRESSURE-RESPONSIVE MEANS INCLUDING A CLOSED HYDRAULIC CHAMBER, PISTON MEANS IN SAID CHAMBER, SPRING MEANS FOR ACTING ON SAID PISTON MEANS FOR APPLYING PRES- 